This invention relates to internal combustion engine control systems and more particularly to control systems for engines having electronically controlled throttles.
As is known in the art, control strategies for internal combustion engines have evolved from purely electromechanical strategies to increasingly more complex electronic or computer controlled strategies. Spark-ignited internal combustion engines have traditionally used airflow as the primary control parameter, controlled by a mechanical linkage between a throttle valve and an accelerator pedal. Fuel quantity and ignition timing, originally mechanically controlled, were migrated to electronic control to improve fuel economy, emissions, and overall engine performance. Electronic throttle control systems have been developed to further improve the authority of the engine controller resulting in even better engine performance.
Electronic throttle control replaces the traditional mechanical linkage between the accelerator pedal and the throttle valve with an xe2x80x9celectronicxe2x80x9d linkage through the engine or powertrain controller. Because of this electrical or electronic linkage, this type of strategy is often referred to as a xe2x80x9cdrive by wirexe2x80x9d system. A sensor is used to determine the position of the accelerator pedal which is input to the controller. The controller determines the required airflow and sends a signal to a servo motor which controls the opening of the throttle valve. Control strategies which imitate the mechanical throttle system by controlling the opening of the throttle valve based primarily on the position of the accelerator pedal position are often referred to as pedal follower systems. However, the ability of the controller to adjust the throttle valve position independently of the accelerator pedal position offers a number of potential advantages in terms of emissions, fuel economy, and overall performance.
An engine control strategy typically has a number of operating modes, such as idle, cruise, engine speed limiting, dashpot, normal driving, etc. The various control modes may or may not use the same or similar primary control parameters. Furthermore, modes of operation often use different control strategies, which may include open loop and/or closed loop feedback/feedforward control strategies. Likewise, different strategies may utilize proportional, integral, and/or derivative control with control parameters tuned to particular applications or operating conditions.
To provide optimal driving comfort and robust control of the engine under varying conditions, it is desirable to provide smooth transitions between control modes. In particular, it is desirable to provide smooth or seamless transitions between idle control mode, where the accelerator pedal is not depressed, and a normal driving mode where the accelerator pedal is depressed. Torque-based ETC (electronic throttle control) systems typically schedule a throttle position based on the driver""s accelerator pedal position by first mapping pedal position, along with variables such as engine speed and vehicle speed, to an equivalent torque request. This so-called driver demand torque is then used to schedule throttle plate position, air fuel ratio, spark ignition timing and any other torque-influencing actuators in use (e.g. CMCV, VCT) in an optimal fashion to deliver this torque to the drive-train. When the driver releases the accelerator pedal to the zero, or closed pedal, position, this part pedal control system relinquishes control to one or more controllers which aim to provide acceptable coast-down rates and idle speed control. Together, these are referred to as closed pedal control. When the driver tips back in to the accelerator pedal, a transition occurs between the active closed pedal control and the driver demand part pedal control.
The problem addressed by the current invention is the following: At the time the driver tips in from closed pedal, the mapped driver demand torque may not match the torque which the engine was producing at closed pedal, causing a step change in the torque to be delivered by the engine. In accordance with the present invention, a method is provided to determine a replacement for the driver demand torque such that the initial part pedal torque matches the torque at closed pedal and so that in a minimal amount of time the part pedal torque will match the output of a driver demand table.
In accordance with one feature of the invention, a method is provided for controlling an electronically controlled throttle of an internal combustion engine. The method includes determining driver demanded torque, xcfx84dd. The time rate of change d(xcfx84dd)/dt in such determined driver demanded torque is determined from determined driver demanded torque, xcfx84dd. A control signal, xcfx84, to the electronically controlled throttle is provided, such control signal xcfx84 being a function of: a previously provided control signal to the electronically controlled throttle, xcfx840; an offset, xcex94xcfx84, of the previously provided control signal, xcfx840, from the determined driver demanded torque, (xcfx84ddxe2x88x92xcfx840); and the determined time rate of change d(xcfx84dd)/dt).
In one embodiment, torque is calculated such that the shape of the part pedal torque substantially tracks that of the driver demanded torque. In this embodiment, the control signal, xcfx84, is provided by summing the prior control signal, xcfx84o, with a term xcfx84xe2x80x2, the term xcfx84xe2x80x2 being:
(A) relatively small (i.e., 0 less than xcfx84xe2x80x2 less than d(xcfx84dd)/dt) when:
(a) the sense of the determined time rate of change d(xcfx84dd)/dt is positive; and
(b) the control signal, xcfx84, is greater than the currently determined driver demanded torque xcfx84dd;
(B) relatively small (i.e., d(xcfx84dd)/dt less than xcfx84xe2x80x2 less than 0) when:
(a) the sense of the determined time rate of change d(xcfx84dd)/dt is negative; and
(b) the control signal, xcfx84, is less than the currently determined driver demanded torque xcfx84dd;
(C) relatively large (i.e., 0 less than d(xcfx84dd)/dt less than xcfx84xe2x80x2) when:
(a) the sense of the determined time rate of change d(xcfx84dd)/dt is positive; and
(b) the control signal, xcfx84, is less than the determined driver demanded torque xcfx84dd; and
(D) relatively large (i.e., xcfx84xe2x80x2 less than d(xcfx84dd)/dt less than 0) when:
(a) the sense of the determined time rate of change d(xcfx84dd)/dt is negative; and
(b) the control signal, xcfx84, is greater than the determined driver demanded torque xcfx84dd.
In a further embodiment, the term, xcfx84xe2x80x2, is provided by determining a factor, xcex1, such factor, xcex1, being a function of an offset, xcex94xcfx84, between the driver demand torque, xcfx84dd, and the control signal, xcfx84, (i.e., xcex94xcfx84=xcfx84oxe2x88x92xcfx84dd), and the sense (i.e., sign or polarity) of the determined time rate of change d(xcfx84dd)/dt. The prior control signal, xcfx84o, is summed with the product of the determined factor, xcex1, and xcex94xcfx84dd to produce the control signal, xcfx84. That is, xcfx84=xcfx84o+xcex1xcex94xcfx84dd=xcfx84o+xcex1d(xcfx84dd)/dt xcex94t.
In one embodiment, xcex1 is 1+f(xcex94xcfx84) when the sense of the determined time rate of change d(xcfx84dd)/dt is positive (i.e., an acceleration is being demanded) and where xcex1 is 1xe2x88x92f(xcex94xcfx84) when the sense of the determined time rate of change d(xcfx84dd)/dt is negative (i.e., a deceleration is being demanded) and where:                                           f            ⁡                          (              Δτ              )                                =                      -            M                          ,                  xe2x80x83                ⁢                              when            ⁢                          xe2x80x83                        ⁢                          (              Δτ              )                                 less than                                     -              B                                                                        =                                                    +                M                            ⁢                              xe2x80x83                            ⁢              when              ⁢                              xe2x80x83                            ⁢                              (                Δτ                )                                       greater than                                           +                B                                                    ;                  xe2x80x83                ⁢        and                                          =                                                    (                                  M                  /                  B                                )                            ⁢                              (                Δτ                )                            ⁢                              xe2x80x83                            ⁢              when              ⁢                              xe2x80x83                            ⁢                                                -                  B                                                       greater than                           (              Δτ              )                         greater than                                           +                B                                                    ;            
where M and B are constants and the magnitude of M is less than or equal to 1 and B is greater than 0.